Mysterious rings around a space rock that may have been carved by a secret moon: ScienceAlert
The secret lives of minor planets may be more complex and fascinating than we thought.
A pair of thin rings orbiting an asteroid-like piece of rock in the cold regions of space outside Jupiter are likely nurtured by a small, invisible moon, scientists have discovered.
The rock was named Chariclo, a type of minor planet known as a centaur, an asteroid-like body that orbits the sun in space between Jupiter and Neptune (rather than between Jupiter and Mars, where the asteroid belt extends).
Chariclo, with a diameter of just 250 kilometers (155 miles), is the only known ringed centaur or asteroid, containing not one, but two rings.
How asteroids maintain their rings is unknown. But, led by astronomer Amanda Sicaphos of the Planetary Science Institute, a pair of scientists ran simulations and found that small moons are a plausible explanation.
“Rings around minor planets have only recently been discovered, and only a few such systems are currently known,” says Sicafos.
“There has been significant research into dazzling rings around giant planets, however, the mechanisms of ring formation and evolution around small objects are not well understood. We have shown that one possibility for thin rings around small objects is that they are sculpted by a small satellite.”
Rings in the solar system are actually not uncommon. Half of the planets (Jupiter, Saturn, Uranus, and Neptune) have known rings, and some dwarf planets also have known rings. They typically consist of tiny dust and ice grains orbiting around the body’s equator, bound in a gravitational orbit, like a disintegrated moon.
We’ve found an increasing number of asteroids with moons, so planetesimals with small rings aren’t the strangest things imaginable. But there are two very clearly defined episodes, as Chariclo did, that are interesting.
Sicafos and her colleague, computer scientist Mark Lewis from Trinity University, wanted to know what makes the rings so tidy.
They ran a series of N-body simulations using modified code originally designed to understand Saturn’s rings, and changed various parameters to try to replicate Chariclo’s system.
The researchers found that a single small moon with a diameter of 1 kilometer (0.62 miles) can retain gossamer rings similar to those seen orbiting Chariclo, shaping them and maintaining a gap between them in a manner similar to Saturn’s shepherd moons. In fact, such a moon may be necessary.
“Planetary rings will naturally spread out or disperse over time. Chariclo displays two thin rings, a few kilometers across. For the rings to remain this thin, there must be a mechanism to confine matter and prevent it from dispersing.” says Sicaphos.
“We actually showed this in the paper by simulating a Chariclo-like ring system that does not contain a satellite, and we find that the width of the rings increases linearly with time. This is in contrast to the situation when there is a satellite in resonance with the ring material, which acts to confine the rings.” In a kilometer-sized display it is observed.”
Interestingly, the two rings are very close to Chariklo, known as the Roche limit. This is the critical distance at which the rings must begin to come together under the influence of gravity and form the moons themselves. However, a small moon can keep the ring turbulent enough to remain a ring. This is another factor that could be in favor of the young moon.
Unfortunately, given Chariclo’s small size and distance, and how small any moon is, we won’t be able to get any images of such a moon without sending a mission a little closer. There may also be an indirect way to detect whether or not there is a moon orbiting Chariklo and observe its rings.
It is also not clear what the rings are made of. Ice may be a very large percentage, but we don’t know the size of the molecules or how they interact. Knowing these details will help figure out what exactly is going on with this fascinating creature.
The research was published in Planetary Science Journal.